Let's see - My house was built in June of 2013, so it's almost brand new. I think these issues have existed for a while but I was never doing anything intensive enough to notice any of the issues. I'd notice the occasional inconsistent speed but never keyed into it until I tried downloading larger files the last few weeks.
I checked the cables that run to the panels and they all say Cat 5e.
The dmark cable appears to come straight from the box and into my basement. Maybe a grand total of 8 feet of cable, with the remaining cabling running a max of 100 feet. So all in, the longest line is maybe 150 feet. Or it should be.
To clarify, the demark cable runs into the basement and has a connector. I then hook it into a router and that router hooks into the 4 prewired cables that run into the living area of the house.
I've attached some photos - I'm hoping that makes things look a little more clear. I didn't include a photo of the "box" outside, I can't get into it. Escuse the rat's nest of cables, I'm hoping ugly doesn't affect anything.